Dew point indicators



1968 P. E. NOKES v DEW POINT INDICATORS Filed Oct. 22, 1965 TIM:

TEMPERAn/RE Inventor Philip E NokEs By his Attornqy United States Patent3,416,355 DEW POINT INDICATORS Philip E. Nokes, Beverly, Mass., assignorto United Shoe Machinery Corporation, Boston, Mass., a corporation ofNew Jersey Filed Oct. 22, 1965, Ser. No. 501,781 1 Claim. (Cl. 7317)ABSTRACT OF THE DISCLOSURE Apparatus for determining the dew point of anatmosphere confined in an enclosed chamber comprising an elongatedmember having a light source, a molded plastic member having areflective surface and a thermocouple embedded therein, and a lightresponsive member mounted on one end thereof.

This invention relates to apparatus for determining the dew point of anatmosphere, and, more particularly, to apparatus for preciselydetermining the dew point in a controlled, humidified atmosphereartificially created in an enclosed chamber.

The dew point or dew point temperature of an atmosphere is thetemperature corresponding to saturation (100% relative humidity) for agiven weight of vapor. Any lowering of temperature from the dew pointproduces a contraction of volume and partial condensation. That is, thedew point of an atmosphere is the temperature at which a given sample ofmoist air will become saturated and deposit dew.

The dew point indicator taught by the subject invention was specificallyintended for use in determining the dew point in a chamber used to heatset shoe uppers. Although the apparatus of this invention is applicableto all situations wherein it is desired to determine the dew point of anatmosphere and particularly an enclosed atmosphere, a statement of the'heat setting application exemplifies the need filled by the inventionand the deficiencies of prior art apparatus.

A commonly employed method of heat setting shoe uppers comprises heatingthe upper in a high-temperature moist atmosphere and thereafter dryingthe upper in a dry atmosphere. These operations are performed subsequentto lasting to impart the shape of the last to the shoe upper. Thepurpose of the heating operation is to heat moisture and fat liquors inthe upper to soften the fibers thereof whereby to remove residualstresses therein. The combination of moisture and heat are the primaryconstituents required to accomplish stress relief, The subsequent dryingoperation removes moisture from the upper and imposes stresses whichthereafter produce a permanent reproduction of the shape of the last. Inone application of the method, individual chambers are used to enclosethe moist and dry atmospheres. The initial step in the method is aheating operation which must be accomplished without drying the leather.Accordingly, the humidity level of the moist atmosphere must bemaintained at a magnitude sufiicient at least to insure moistureequilibrium between the atmosphere and the leather thereby to preventdrying of the leather. This is accomplished by maintaining the dew pointof the moist atmosphere above the temperature of the upper. The resultof this step is to precipitate a film of water on the upper. The heatedatmosphere condenses the water film and the heat of condensation resultsin rapid heating of the upper. The ability to determine the dew pointwithin the chamber is thus critical.

The two steps of the above-described application of the method may, inan alternative embodiment, be combined in a unitary step employing asingle atmosphere to both heat and dry the lasted upper. This isaccomplished by the use of a high temperature moist atmosphere the dewpoint and temperature of which are controlled such that, for a givenexposure interval, the temperature of the upper is elevated from a levelbelow the dew point to a level thereabove. That is, when an upper isintroduced into the chamber, the dew point of the chamber is above theinitial temperature of the upper. Thus, initially, the temperature ofthe upper is raised without withdrawing moisture therefrom. When thetemperature of the upper is raised above the dew point of the atmosphereby heat transferred thereto from the atmosphere, moisture is thereafterremoved from the upper. The dew point of the atmosphere within thechamber is thus of utmost criticality in this embodiment.

In the commercial use of the heat setting method and apparatus describedabove, means must be provided which permit frequent checking of the dewpoints within the enclosed chambers. One possible laboratory techniquefor determining the dew point is by the use of a thermocouple pyrometer.A thermocouple pyrometer consists essentially of a thermocouple of twodifferent metals or alloys the wires of which are fused together at oneend to form the measuring (hot) junction which is exposed to thetemperature to be measured. The other ends of the wires are connected toan indicating instrument such as a multivoltmeter or potentiometer. Theelectromotive force induced by the difference in temperature between thedifferent metals or alloys is proportional to'the temperaturedifference. Temperature-EMF data for thermocouples is readily availableto make the necessary conversion of data. Thus, the temperature withinan enclosed chamber can be determined by this device. The dew pointtemperature may be determined by plotting the temperatures obtainedagainst time, see FIG. 4 of the drawings. The dew point temperature isthat point on the graph of FIG. 4 at which the temperature remainsconstant for a relatively extended period. After the dew point is past,the temperature will again being to rise. The reason for a sustainedconstant temperature at the dew point is that heat is being absorbed inthe evaporation of condensation and is not available to elevate thetemperature of the enclosed atmosphere.

The thermocouple pyrometer technique is an accurate laboratorytechnique. However, it requires the services of a skilled artisancapable of operating and interpreting a multivoltmeter or potentiometerto determine the plateau in temperature rise which denotes the dewpoint. Such a skilled artisan is not normally available in a shoefactory where the above described heat setting method would bepracticed.

The commonly employed technique for determining dew point is by coolinga flat polished metal surface until it becomes clouded with a film ofwater; the dew point being the temperature at which the film appears.However, this technique is not adaptable for use within an enclosedchamber where visual access is not available.

The teachings of the prior art do not, in fact, provide apparatus bywhich the dew point of an enclosed atmosphere can be readily determinedby an unskilled artisan. A number of alternate techniques to thethermocouple pyrometer discussed above are taught by the prior art fordetermining temperature. However, each of these techniques requires askilled artisan to determine the dew point by the use thereof.

Accordingly, it is an object of the present invention to provideapparatus for precisely and easily determining the dew point of anatmosphere.

To this end and in accordance with a feature of this invention there isprovided apparatus for determining the dew point of an atmospherecomprising a conducting member having a reflective surface and a meansmounted therein for determining the temperature thereof, a light sourcedirected at said reflective surface, a light responsive memberpositioned in the path of light reflected by the reflective surface whensaid surface is free of moisture, and means responsive to the activationof said light responsive member to record the same.

The above and other features of the invention including various andnovel details of construction and combinations of parts will now be moreparticularly described with reference to the accompanying drawings andpointed out in the claim. The principles and features of this inventionmaybe employed in various and numerous embodiments without departingfrom the scope of the invention.

In the drawings:

FIG. 1 is a side elevation, partly in section, of apparatus embodyingfeatures of the present invention;

FIG. 2 is a plan view of the light source, reflector means, and lightresponsive means employed in the embodiment of this invention generallyillustrated in FIG. 1;

FIG. 3 is an electrical wiring diagram of the apparatus illustrated inFIG. 1; and

FIG. 4 is a graph illustrating the dew point plateau in atemperature-time plot.

The apparatus of this invention comprises a light source 10, areflective surface 12 formed on a mounting unit 14 and a lightresponsive member 16 all of which are utilized in combination with athermocouple pyrometer 2 whereby to facilitate the determination of thedew point of an atmosphere without the need to interpret the readings ona multivoltmeter or potentiometer. The light source and light responsivemember 16 are both mounted in a unitary mounting block 20. The mountingblock 20 and mounting unit 14 are mounted at spaced positions on the endportion of an elongated hollow member 24. The elongated member 24 may beused as a handle to insert the mounting block 20 and mounting unit 14into a chamber 22 housing an atmosphere the dew point of which is to bedetermined.

The mounting block 20 and mounting unit 14 are positioned on the member24 such that light emanating from the light source 10 will be directedat the reflective surface 12 on the mounting unit 14. The reflectivesurface 12 is concave and is so positioned on the member 24 as toreflect a beam of light from the light source 10' in the direction ofthe light responsive member 16 whereby to activate said light responsivemember 16.

In the use of the apparatus of this invention to determine the dew pointof an enclosed atmosphere, the elongated member 24 is inserted into thechamber 22 whereby to position the mounting block 20 and mounting unit14 in exposed relation to the atmosphere. The temperature of theenclosed atmosphere is initially higher than the temperature of themounting unit 14 and, therefore, also for the reflective surface 12thereon. Likewise, the temperature of the unit 14 and surface 12 isbelow the dew point of the enclosed atmosphere. In the heat settingapplication discussed above, the temperature within the chamber 22 is inthe 220 F. to 375 F. range while the mounting unit is at roomtemperature when it is inserted. Accordingly, moisture initially will becollected on the unit 14 and the surface 12 as a result of thistemperature differential. The film of water thus formed on thereflective surface 12 results in the diffusion of light directed thereatfrom the light source 10. That is, although the water vapor istransparent when suspended in the atmosphere, it results in diffusion ofthe light beam cast upon the reflective surface 12 rather than in thereflection thereof. Accordingly, light will not be reflected in thedirection of the light responsive member 16 with suflicient candle powerto activate the member 16. It should be noted that although in theembodiment illustrated in FIG. 1 both the mounting unit 14 and themounting block 20 are inserted into the enclosed chamber, only themounting unit 14 need be exposed to the atmosphere.

Further exposure of the mounting unit 14 to the enclosed atmosphere willresult in the transfer of heat to the reflective surface 12 from theatmosphere and, accordingly, in an increase in the temperature thereof.When the temperature of the reflective surface 12 is elevated to the dewpoint of the atmosphere, the water film on the reflective surface 12will evaporate. Thus, when the temperature of the reflective surface 12corresponds to the dew point temperature of the atmosphere, light willbe reflected by the surface 12 in the direction of the light responsivemember 16 whereby to activate the same. The activation of the lightresponsive member is recorded on an indicating instrument 40 which maybe of any convenient design. The electrical connection between themember 16 and instrument 40 is accomplished by wires in the hollowmember 24. The point at which the reflective surface reaches the dewpoint is thus recorded without the necessity of reference to atemperature graph or potentiometer interpretation.

The exact temperature of the reflective surface 12 corresponding to thedew point of the atmosphere is recorded by means of a thermocouple 50,50 housed in the mounting unit 14 adjacent the surface 12 and anassociated potentiometer 54. That is, by a thermocouple pyrometer whichfunctions in the manner described above. In the preferred embodiment,the mounting unit comprises a solid molded plastic member in which thethermocouple is mounted such that the juncture thereof is adjacent thereflective surface 12. The reflective surface comprises a silvercoating. The plastic member insulates the thermocouple from thetemperature of the atmosphere. Accordingly, the thermocouple isessentially influenced only by heat transferred thereto from thereflective surface 12. The temperature of the surface 12 at the dewpoint is thus recorded. The lead wires for the thermocouple are alsohoused in the hollow member 24.

In the use of the apparatus, an operator need only record thetemperature level on the potentiometer at the time the activation of thelight responsive number 16 is registered on the instrument 40. There isno need to apply the skill required to interpret the potentiometerreading to recognize the temperature plateau which denotes the dew pointas shown in FIG. 4.

The circuitry delineated in FIG. 3 illustrates the cooperation betweenthe light source 10, reflective surface 12 and light responsive member16. The electrical connection between the light responsive member 16 andthe indicating instrument 40 is also shown. The thermocouple 50, 50 mustbe located in close proximity to the reflective surface 12 in order toensure comparative temperature levels. This is shown in FIG. 3 as wellas FIG. 2. The remainder of the circuitry shown in FIG. 3 denotes apotentiometer comprising storage cells 60, 62, a rheostat 64, a seriesof resistance members 66, a microammeter 68 and a key 70.

Having thus described my invention, what I claim as new and desire tosecure by Letters Patent of the United States is:

1. Apparatus for determining the dew point of an atmosphere confined toan enclosed chamber comprising a light source, a mounting unitcomprising a solid molded plastic member having a reflective silvercoated surface and a thermocouple mounted in said plastic member withthe juncture thereof adjacent the reflective surface, a light responsivemember, said light source, mounting unit and light responsive memberbeing mounted on one end of an elongated member such that light emittedfrom said light source will be directed at said mounting unit and light5 reflected by said mounting unit will be directed at said lightresponsive member when the said end of the elongated member is insertedinto an enclosed chamber and the 'light source activated, meansresponsive to the actuation of said light responsive member to indicatethe same, and means for recording the temperature measured by thethermocouple when the light responsive member is actuated.

